Concerning the motor driving apparatus, there is a known configuration in which when an alternate-current (AC) voltage is converted into a DC voltage by a converter and a DC link voltage generated by a capacitor configured to smooth the DC voltage is supplied to the inverter unit, the DC link unit configured to output the DC link voltage and the inverter unit are interconnected by the short bar that is a short-circuiting component between terminals (e.g., Japanese Unexamined Patent Publication No. JP-A-2009-225497). FIG. 1 illustrates a configuration example of the conventional motor driving apparatus. In the example of the conventional motor driving apparatus 1000, two inverter units 1020 and 1030 are connected to one converter unit 1010. The converter unit 1010 includes a DC link unit (not illustrated), and output terminals 1011 and 1012 of the DC link unit are exposed to the outside. The first inverter unit 1020 includes two input terminals 1021 and 1022, and the second inverter unit 1030 includes two input terminals 1031 and 1032.
The DC link voltage from the DC link unit disposed in the converter unit 1010 is input to the first and second inverter units 1020 and 1030. In the conventional example illustrated in FIG. 1, electric connection between the converter unit 1010 and the inverter units 1020 and 1030 is carried out through short bars 1041 and 1042. In other words, the terminals 1011, 1021, and 1031 are connected through the short bar 1041, while the terminals 1012, 1022, and 1032 are connected through the short bar 1042. In such a conventional motor driving apparatus, the DC link voltage that is an inter-terminal voltage of the capacitor configured to smooth the DC voltage is measured by the DC link voltage detection unit directly connected to the smoothing capacitor.
FIG. 2 illustrates an example of a circuit diagram of the conventional motor driving apparatus. As illustrated in FIG. 2, an AC voltage from an AC power source 1001 is converted into a DC voltage by the converter unit 1010, and smoothed by the smoothing capacitor 1014 disposed in the DC link unit 1013. The smoothed DC link voltage is supplied through the short bar 1041 for connecting the terminals 1011, 1021, 1031, and 1091 and the short bar 1042 for connecting the terminals 1012, 1022 1032, and 1092 to the first inverter unit 1020, the second inverter unit 1030, and an N-th inverter unit 1090.
In the conventional motor driving apparatus 1000 illustrated in FIG. 2, the DC link voltage is detected by the DC link voltage detection unit 1015 directly connected to the terminals 1011 and 1012 of the capacitor 1014. Whether there is any abnormality of the capacitor 1014 or whether power for the AC power source 1001 has been cut can be detected by the DC link voltage detection unit 1015.
However, in the conventional motor driving apparatus, an abnormality caused by disconnection of the short bar or the like may not be detected. For example, in the short bar 1041, even when disconnection occurs at a short bar 1041a for connecting one terminal 1011 of the DC link unit 1013 to one terminal 1021 of the first inverter unit 1020, the DC link voltage detection unit 1015 may not detect a voltage applied between the terminals 1021 and 1022 of the first inverter unit 1020 because the detection unit 1015 is directly connected to the capacitor 1014. As a result, even when an abnormality occurs at the short bar 1041a that is a part of the short bar 1041, the abnormality may not be detected.
At which of a plurality of parts 1041a to 1041c and a plurality of parts 1042a to 1042c respectively constituting the short bars 1041 and 1042 abnormality has occurred may not be detected. As a result, in a real application, when disconnection occurs at a short bar in a robot or a machine tool constituting a gravity axis, a dangerous situation may occur. Specifically, an axis after the disconnected place of the short bar may fall.
As described above, in the conventional motor driving apparatus, even when abnormality occurs at the short bar for connecting the DC link unit to the inverter unit, the abnormality may not be detected.